When is a Cup not a Cup?

All three of my sons and I are in Taekwondo, last night after an evening of sparring I asked my 7 year old, while he sucked on a slushy, if he had worn his cup while sparring.  The answer from him was a NO, while trying to explain to him that he MUST wear his cup, my 4 year old piped in to let me know that he and the 8 year old had to share a cup. (Forgetting they did share a single slushy from a single cup) I explained to him that both the 7 and 8 year old had their own cups.  It was then my friend, who was visiting, pointed out that we were talking about two different kinds of  cups. =)  I want Grandchildren, so those boys of my better start wearing their cup!